Energy transport in peptide helices

Abstract

We investigate energy transport through an ␣-aminoisobutyric acid-based 310-helix dissolved in chloroform in a combined experimental-theoretical approach. Vibrational energy is locally deposited at the N terminus of the helix by ultrafast internal conversion of a covalently attached, electronically excited, azobenzene moiety. Heat flow through the helix is detected with subpicosecond time resolution by employing vibrational probes as local thermometers at various distances from the heat source. The experiment is supplemented by detailed nonequilibrium molecular dynamics (MD) simulations of the process, revealing good qualitative agreement with experiment: Both theory and experiment exhibit an almost instantaneous temperature jump of the reporter units next to the heater which is attributed to the direct impact of the isomerizing azobenzene moiety. After this impact event, helix and azobenzene moiety appear to be thermally decoupled. The energy deposited in the helix thermalizes on a subpicosecond timescale and propagates along the helix in a diffusive-like process, accompanied by a significant loss into the solvent. However, in terms of quantitative numbers, theory and experiment differ. In particular, the MD simulation seems to overestimate the heat diffusion constant (2 Å 2 ps ؊1 from the experiment) by a factor of five.energy dissipation ͉ time-resolved IR spectroscopy ͉ peptide helix ͉ nonequilibrium molecular dynamics simulation

Two-Dimensional Spectroscopy of Extended Molecular Systems: Applications to Energy Transport and Relaxation in an α-Helix

“…Since in the parametrization of our model we used the fluctuations of the vibrational constants in NMA-d 7 in heavy water, we probably overestimated the importance of the fast water dynamics: the surrounding of the amide groups in a helix is somewhat less dominated by water than in a single NMA-d 7 molecule. In addition, our approach neglects the role of slow conformational changes in the helix; at least for short helices such changes have been seen.…”

“…In particular, the analogues of the NOESY variant of 2DNMR allow for the study of dynamics, because they involve a waiting time t 2 that may be controlled at the femtosecond time scales, thus allowing one to take snapshots of a system while it evolves. 2,3 Examples of systems that have been studied using 2DIR or 2Dvis spectroscopies with nonzero waiting times include relatively simple few-level systems, such as the coupled amide I and amide II vibrations in N-methylacetamide (NMA) 4 and vibrations in other small organic molecules, 5 as well as extended systems with a multitude of levels, such as the amide I band in polypeptides or proteins, 6,7 the excitonic transitions in the photosynthetic Fenna-Matthew-Olsen complex, 8 and the excitonic transitions in double-wall molecular nanotubes. 9 In the simplest situation, with only two interacting vibrational or electronic states of interest, it is rather straightforward to obtain information about their coupled dynamics from the waiting time dependence of the 2D spectrum.…”

Heat transfer in protein–water interfaces

“…5 Chemical and photochemical reactions occurring at specific spots in biomolecules can result in large increases in temperature in very small volumes. Transient photon experiments, where photon absorption is converted to vibrational energy, show that the temperature rise resulting from this process can be very significant, between 500 and 1000 K. 6,7 Recent work on the Ca 2+ -ATPase embedded in the sarcoplasmic reticulum has suggested that this enzyme can -under working conditions -release significant amounts of heat. Using micro-thermometers it was found that thermal gradients of the order of 10 5 K/m can develop between regions separated by tens of micrometers.…”

Vibrational Energy Transport through a Capping Layer of Appropriately Designed Peptide Helices over Gold Nanoparticles

“…As in our previous studies [15][16][17][18] the isotope labels are placed by incorporating 13 C-l-Ala, since this amino acid is readily available commercially and does not destabilize the 3 10 -helix significantly. An urethane moiety was inserted between the linking group and the actual peptide to have an intrinsically spectrally resolved C=O group at the beginning of the helical chain.…”